Resettable fuse

ABSTRACT

A resettable fuse utilizing a heat-shrinkable retractor which functions to pull a movable contact away from a fixed contact against a snap action retention therebetween. A heater within the fuse is connected in series with the contacts so as to effect the desired heat shrinking of the retractor when the current flow therethrough reaches a preselected value. A manually operable restretching device is provided for restretching the heatshrinkable retractor for resetting of the fuse. The manually operable structure is limited in its movement by a wall portion of the fuse for controlling the manipulation thereof.

" United States Patent Healy Sept. 16, 1975 RESETTABLE FUSE Primary Examiner--.l. D. Miller 1 t R bert M. Rt. 2, B 359, [761 f gifl' g Assistant Examiner-Fred E. Bell Attorney, Agent, or FirmWegner, Stellman, McCord, [22] Filed: Sept. 16, 1974 Wiles & Wood App]. No.: 506,185

[57] ABSTRACT A resettable fuse utilizing a heat-shrinkable retractor which functions to pull a movable contact away from a fixed contact against a snap action retention therebetween. A heater within the fuse is connected in series with the contacts so as to effect the desired heat shrinking of the retractor when the current flow therethrough reaches a preselected value. A manually operable restretching device is provided for restretching the heat-shrinkable retractor for resetting of the fuse. The manually operable structure is limited in its movement by a wall portion of the fuse for controlling the manipulation thereof.

5 15 Claims, 8 Drawing Figures PATENIEBSEP rams a. -Z///////////////A RESETTABLE FUSE 1. Field of the Invention This invention relates to resettable fuses'and in particular to resettable fuses utilizing a heat-shrinkable retractor.

2. Description of the Prior Art The use of resettablefuses' in' controlling electrical current is a desideratum as it avoids the necessity of replacing a burned out unit and rather, permits the user to merely reset the original fuse once the overcurrent situation is remedied. A large number of difi'erent types of such resettable fuses have been developed over the years. Illustratively, as shown in US. Pat. No. 1,560,597 of Ernest Meierjohan, an automatic cut-out is provided wherein a wire 18 expands lengthwise to press outwardly against a spring finger 14 to release a lip 'l6fromengagement with stop collar 17 to cause an opening of the circuit. v

In Durward S. Rivers US. Pat. No. 2,044,448, a circuit interrupter is provided wherein a wire 30 expands upon the current flow exceeding the preselected amount to rock a lever 22 ,to .release the connector end 20. Upon coolingof the wire and contraction back to a straightline position, the mechanism is arranged to preventresetting of the lever 22. In Durward S. Rivers et al. U.S. Pat. No. 2,044,449, the expandable wire rocks a bar 14. The fuse is reset by means of a shaft 30 and provides the safety feature of the melting of the wire in case the device fails to trip.

A number of current control devices have recently been developed utilizing a TiNi compound which has a memory characteristic such that when the material is heated to a critical temperature depending on the specific composition of the compound, it returns to an undeformed condition from a previously deformed state. The, formulation and functioning of such compositions is disclosed in US. Pat. No. 3,174,851 of William J. Buehler et al. In US. Pat. No. 3,403,238, of William J. Buehler et al., a conversion of heat energy to mechanical energy is disclosed.

In US. Pat. No. 3,516,082, of Roy G. Copper, temperature sensingdevices aredisclosed utilizing such an intermetallic composition for actuating an audio-visual signalling device. The devicesare arranged to be returned to the original shape at a temperature below the critical temperature'such as by use of suitable spring means. i v

Cleon F. Freydiscloses, in US. Pat. No. 3,594,673, a-flasher switch which utilizes a thermal expansion wire exerting a buckling force on a snap vane which carries a movable contact of a switch.

James R. Wilson discloses, in US. Pat. No. 3,594,674 and 3,594,675, temperature-responsive devices utilizing such a memory composition in controlling current flow. In US. Pat. No. 3,684,803, James Wilson et al. disclose another form of such a temperature-responsive device with means biasing a movable contact into one position when the control member has a distorted shape. 1

US. Pat. No. 3,652,969 of James R. Wilson et al, dis

- closes a method and apparatus for stabilizing and employing temperature-sensitive material exhibiting such martensitic" transitions. The method includes subjecting temperature cycles with the material in' the overstressed condition so as to subsequently cause the material to operate through work cycles with no loss of dimension stability;

Gideon A. Du Rocher, in US. Pat. No. 3,676,815,

discloses a thermally sensitive control utilizing such a composition in the force-applying member acting on a switching means.

Hugh Jean Tyler, in U.S.- Pat. No. 3,684,994, discloses a hot wire release device having a mechanical shape memory with the supp orted portions arranged to not react to heat so that the wire achieves a thermal balance throughout. In US. Pat. No. 3,703,693, of R0- bert N. Levinn, the length of the wire is changed corresponding to the level of liquid in a tank by a change in the heat transfer characteristics of the material surrounding the'wire as a function of the liquid level.

In Gideon A. Du Rocher US. Pat. No. 3,707,694, a

SUMMARY OF THE INVENTION The present invention comprehends an improved resettable fuse utilizing such a martensitic transition heatshrinkable retractor for controllin g the disruption of an electrical current. The fuse retractor irfcl'utlesjafixed end, a movable end connected to the movable contact of a switch portion of the fuse, and a rectilinear midportion normally stretched between the fixed and r'novable ends. With the retractor in the stretched condition, the movable contact is normally releasably held in electrical connected association with the fixed contact as by a snap fastener connectorj A heater means is connected in series with the switch contacts, and in thermal transfer association withthe' retractor mid-portion. Thus, the heater carries'the electrical current being controlled by the fuse and is preselected so as to heat the retractor to the transition, or critical, temperature at the rated current of the fuse, thereby causing the retractor to return to its undeformed state, and in doing so, separate'the movable contact from the fixed contact against'the retaining action of the holding means.

The fuse further includes a manually operable means for selectively restretching the rectilinear mid-portion of the retractor upon a cooling of the heater means and retractor to permit the holding means to again hold the movable contact in electrical association with the fixed contact. The manually operable means may comprise a tubular element coaxially surrounding the retractor portion, and the heater means may be disposed within the tubular element. The heater means may extend spirally about the retractor mid-portion.

Further in the illustrated embodiment, means are provided for limiting the movement of the manually operable means, and illustratively comprise a wall element having an opening therethrough with a manipulating portion of the manually operable means extending through the opening. The wall means further defines means for positioning the manually operable means in alignment with the retractor rectilinear midportion for maintained accuracy in the restretching operation. it

The length of the retractor is preselected to positively withdraw the movable contact from the snap fastener holding means to prevent electrical reconnection until such time as the retractor is restretched by the manually operable means. The force generated by the shrinking of the retractor is relatively high and, thus, a positive snap-type holding means is employed to effect a positive electrically conductive connection between the contacts in the current-carrying condition of the fuse.

The fuse construction is extremely simple and economical while yet providing an improved accurate resettable fuse operation as discussed above.

BRIEF DESCRIPTION OF DRAWING Other features and advantages of the invention will be apparent from the following descriptiontaken in connection with the accompanying drawing wherein:

FIG. 1 is a side elevation of a resettable fuse embodying the invention; 7 I

FIG. 2 is an enlarged diametric section thereof with the switch contacts in the current-carrying condition;

FIG. 3 is anenlar-ged diametric section thereof with the switch contacts in the current-interrupting condition;

FIG. 4 is a fr gmentary horizontal section taken substantially along the line 4-4 of FIG. 3;

FIG. 5 is a fragmentary vertical section taken substantially along the line 55 of FIG. 2;

FIG. 6 is. a fragmentary horizontal section taken sub.- stantially along the line 6-6 of FIG. 3; n

FIG. 7 is afragmentary horizontal section taken substantially along the line 77.of FIG. 3; and

FIG. 8 is a fragmentary bottom plan view.

DESCRIPTION THE PREFERRED EMBODIMENT In the exemplary embodiment of the invention as disclosed in the drawing, a resettable fuse generally designated 10 includes an insulator body 11 which may be formed of any suitable electrically insulating material, such as glass. The body defines an upper portion 12 and a lower portion 13 provided with a, helical groove 14. A conductive shell 15 formed of material, such as brass, is disposed about the grooved portion 14 to provide electrical contact with a conventional fuse holder socket (not shown). A contact button 16 is provided at the lower end of body portion 13 for providing electrical contact with a complementary central contact of the conventional fuse receptacle (not shown).

Body 1 1 defines a central through bore 17 for receiving means for controlling current flow through the fuse. Contact button 16 includes a cup-shaped metal element 18 mounted to an insulating support 19 and extending upwardly into bore 17 to define at its inner upper end a female snap fastener portion 20. The snap fastener portion 20 effectively defines a fixed contact at the lower end of the fuse adapted for engagement by a movable contact 21 having a male connector portion 22 releasably engageable with the snap fastener portion 20 to provide a maintained electrical association therebetween. Insulator 19 may include a guide portion 23 extending upwardly into a central opening 24; in movprojects outwardly through a top wall 29 carried on the body 11 and having a suitable central opening 30 for extension of the manual grasping portion 28 therethrough, as illustrated in FIG. 2. The grasping portion includes outturned flanges 31 which limit the outward movement thereof as shown in FIG. 3.

Tubular push rod 26 is provided with a recess 32 adjacent its upper end for extension of a heater wire 33 outwardly therethrough and through a suitable passage 34 in the body 11 into electrically connected association with the shell 15. The inner end of the heater wire is connected to movable contact 21 by a suitable solder connection .35.

A retractor wire 36 is joined at its lower end 37 to the solder connection and defines a rectilinear midportion 38 extending upwardly to an upper end portion 39 fixed to the top wall 29 by a connector portion 40. As shown in FIGS. 2 and 3, the heater wire 33 extends spirally about the rectilinear mid-portion 38 of the retractor to be in thermal transfer associationtherewith.

"Retractor wire 36 is formed of a suitable martensitic transition TiNi material having a memory causing it to contract to the contracted arrangement of FIG. 3 from the stretched arrangement of FIG. 2 when the temperature thereof reaches the criticaltemperature of the selected alloy. The manually operable means 25 permits the user to stretch wire 36 to cause the movable contact 22 to have snap-fitted engagement with the fixed portion 20 in the current-carrying arrangement of the fuse, asshown in FIG. 2. When the temperature produced by the high current flow through the electrical heater 33 reaches the critical temperature of the retractor wire 36, a'substantial force is generated in the contraction of i the wire to the normal condition,

thereby forcibly separating the movable contact 21 able contact 21 for guiding the movable contactto and from the snap' fastener contact portion 20 and thereby breaking the circuit to the fuse, as shown in FIG. 3. The movement of the movable contact 21 by the shortening of the retractor 36 is sufficient to effectively positively prevent recontact between movable contact 21 and fixed contact portion 20 in the circuit open condition of FIG. 3. n i I As further shown, the top wall 29 serves as a means for guiding the manual operator portion 28in aligned relationship with the wire portion 38 so as to provide improved resetting of the fuse. At the same time, the movable contact 21 is guided into centered relationship with the snap fastener portion 20 by the guide 23 to as sure a positive reconnection of the contacts in resetting the fuse. The substantial force generated by the shrinking of the retractor wire 36 permits the use of a strong snap action device in maintaining the electrical contact in the current-carrying arrangement of the fuse so as to provide an improved positive current controlling func- 1. A resettable fuse for controlling an electrical current, comprising:

means defining a first, fixed electrical contact;

means defining a second, movable contact;

means for releasably holding the second contact in electrical connected association with the first contact;

a heat-shrinkable retractor having a fixed end, a movable end connected to said movable contact, and a rectilinear mid-portion stretched between said ends;

heater means for carrying electrical current to be controlled in series with said first and second contacts to interrupt the current flow and deenergize said heater means for heat-shrinking said retractor as an incident of the current rising to a preselected value and thereby spacing said movable contact from said first fixed contact; and

manually operable means for selectively restretching said rectilinear mid-portion upon cooling thereof to permit said holding means to again hold said second contact in electrical connected association with the first contact.

2. The resettable fuse of claim 1 wherein said holding means comprises a snap fastener.

3. The resettable fuse of claim 1 wherein said holding means comprises a snap fastener defined by said first and second contact means.

4. The resettable fuse of claim 1 wherein said manually operable means includes a push rod portion having one end engaging said second contact means, and an opposite, manually graspable end.

5. The resettable fuse of claim 1 wherein said manually operable means includes a push rod portion extending parallel to and laterally of said retractor midportion havingone end engaging said second contact means, and an opposite, manually graspable end.

6. The resettable fuse of claim 1 wherein said manually operable means comprises a tubular element coaxially surrounding said retractor mid-portion.

7. The resettable fuse of claim 1 wherein said heater means extends spirally about said retractor midportion.

8. The resettable fuse of claim 1 wherein said heater means extends spirally about said retractor midportion, and said manually operable means comprises a tubular element coaxially surrounding said retractor mid-portion and said heater means.

9. A resettable fuse for controlling an electrical current, comprising:

means defining a first, fixed electrical contact;

means defining a second, movable contact;

means for releasably holding the second contact in electrical connected association with the first contact;

a heat-shrinkable retractor having a fixed end, a movable end connected to said movable contact, and a rectilinear mid-portion stretched between said ends;

heater means for carrying electrical current to be controlled in series with said first and second contacts to interrupt the current flow and deenergize said heater means for heat-shrinking said retractor as an incident of the current rising to a preselected value and thereby spacing said movable contact from said first fixed contact;

manually operable means for selectively restretching said rectilinear mid-portion upon cooling thereof to permit said holding means to again hold said second contact in electrical connected association with the first contact; and

means for limiting the movement of said manually operable means.

10. The resettable fuse of claim 9 wherein said movement limiting means comprises a wall element having an opening therethrough, said manually operable means having a manipulating portion projecting through said wall element.

11. The resettable fuse of claim 9 wherein said movement limiting means comprises a wall element having an opening therethrough, said manually operable means having a manipulating portion projecting through said wall element a preselected distance when the retractor is heat shrunk.

12. The resettable fuse of claim 9 wherein said movement limiting means further defines means for positioning the manually operable means in alignment with said retractor rectilinear mid-portion.

13. The resettable fuse of claim 9 wherein said movement limiting means comprises means for limiting the restretching of said retractor mid-portion to a position wherein said second contact is spaced closely adjacent said first contact.

14. The resettable fuse of claim 9 wherein said manually operable means includes means selectively engaging said first contact means to limit the restretching of said retractor mid-portion to a position wherein said second contact is spaced closely adjacent said first contact.

15. The resettable fuse of claim 1 wherein said heater means is preselected in correspondence with the heatshrinking characteristics of said retractor to provide an accurately calibrated current flow control. 

1. A resettable fuse for controlling an electrical current, comprising: means defining a first, fixed electrical contact; means defining a second, movable contact; means for releasably holding the second contact in electrical connected association with the first contact; a heat-shrinkable retractor having a fixed end, a movable end connected to said movable contact, and a rectilinear midportion stretched between said ends; heater means for carrying electrical current to be controlled in series with said first and second contacts to interrupt the current flow and de-energize said heater means for heatshrinking said retractor as an incident of the current rising to a preselected value and thereby spacing said movable contact from said first fixed contact; and manually operable means for selectively restretching said rectilinear mid-portion upon cooling thereof to permit said holding means to again hold said second contact in electrical connected association with the first contact.
 2. The resettable fuse of claim 1 wherein said holding means comprises a snap fastener.
 3. The resettable fuse of claim 1 wherein said holding means comprises a snap fastener defined by said first and second contact means.
 4. The reseTtable fuse of claim 1 wherein said manually operable means includes a push rod portion having one end engaging said second contact means, and an opposite, manually graspable end.
 5. The resettable fuse of claim 1 wherein said manually operable means includes a push rod portion extending parallel to and laterally of said retractor mid-portion having one end engaging said second contact means, and an opposite, manually graspable end.
 6. The resettable fuse of claim 1 wherein said manually operable means comprises a tubular element coaxially surrounding said retractor mid-portion.
 7. The resettable fuse of claim 1 wherein said heater means extends spirally about said retractor mid-portion.
 8. The resettable fuse of claim 1 wherein said heater means extends spirally about said retractor mid-portion, and said manually operable means comprises a tubular element coaxially surrounding said retractor mid-portion and said heater means.
 9. A resettable fuse for controlling an electrical current, comprising: means defining a first, fixed electrical contact; means defining a second, movable contact; means for releasably holding the second contact in electrical connected association with the first contact; a heat-shrinkable retractor having a fixed end, a movable end connected to said movable contact, and a rectilinear mid-portion stretched between said ends; heater means for carrying electrical current to be controlled in series with said first and second contacts to interrupt the current flow and de-energize said heater means for heat-shrinking said retractor as an incident of the current rising to a preselected value and thereby spacing said movable contact from said first fixed contact; manually operable means for selectively restretching said rectilinear mid-portion upon cooling thereof to permit said holding means to again hold said second contact in electrical connected association with the first contact; and means for limiting the movement of said manually operable means.
 10. The resettable fuse of claim 9 wherein said movement limiting means comprises a wall element having an opening therethrough, said manually operable means having a manipulating portion projecting through said wall element.
 11. The resettable fuse of claim 9 wherein said movement limiting means comprises a wall element having an opening therethrough, said manually operable means having a manipulating portion projecting through said wall element a preselected distance when the retractor is heat shrunk.
 12. The resettable fuse of claim 9 wherein said movement limiting means further defines means for positioning the manually operable means in alignment with said retractor rectilinear mid-portion.
 13. The resettable fuse of claim 9 wherein said movement limiting means comprises means for limiting the restretching of said retractor mid-portion to a position wherein said second contact is spaced closely adjacent said first contact.
 14. The resettable fuse of claim 9 wherein said manually operable means includes means selectively engaging said first contact means to limit the restretching of said retractor mid-portion to a position wherein said second contact is spaced closely adjacent said first contact.
 15. The resettable fuse of claim 1 wherein said heater means is preselected in correspondence with the heatshrinking characteristics of said retractor to provide an accurately calibrated current flow control. 